Electroencephalography remains a fundamental tool in neurological diagnostics, cognitive research, and emerging consumer applications. This comprehensive review critically examines the technological landscape of non-invasive EEG electrodes through a novel comparative framework rather than a conventional chronological analysis. We systematically evaluate wet, semi-dry, and dry electrode technologies across four key dimensions: material and design innovations, signal quality metrics, clinical and research applications, and implementation challenges. Our analysis reveals that while standard wet electrodes remain the gold standard for signal fidelity, they nevertheless require extensive setup, cause notable discomfort—particularly for children and long-term users, and demand ongoing gel reapplication, all of which limit their practicality in many real-world settings. Significant advancements in semi-dry electrodes now address these shortcomings by offering comparable performance with reduced preparation time and enhanced usability. Dry electrodes, despite inherently higher impedance, demonstrate increasing viability for long-term and ambulatory monitoring when paired with appropriate signal processing techniques. This review provides a decision framework for selecting optimal electrode technologies based on specific application requirements, subject characteristics, and recording environments. We identify critical research gaps, particularly in standardization methods, cross-population validation, and integration with emerging materials. As EEG applications expand beyond traditional clinical settings into consumer markets, this review offers valuable guidance for researchers, clinicians, and technology developers navigating the rapidly evolving landscape of EEG electrode technologies.

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